This invention relates to a control device of an AC motor.
In general, a DC motor is extensively employed to drive a servo mechanism which should be controlled with high accuracy over a wide range, because precise speed control can be effected with the DC motor.
However, there has been a strong demand for provision of an AC servo mechanism which uses an induction motor as its driving source, because the induction motor can be readily handled. Heretofore, the speed control of the induction motor is carried out in accordance with a frequency conversion method or the like. However, the conventional methods relate to simple, variable speed control, and therefore cannot obtain driving characteristics with high accuracy. In addition, as for the self-speed-control of the induction motor, a magnetic field orientation control method has been proposed in the art, in which, similarly as in the control principle of a DC motor, spatial magnetic flux is controlled, in a vector mode, by using a slip frequency controlled or pulse width controlled inverter, thereby to drive the induction motor. That is, in this magnetic field orientation control method, the spatial magnetic flux vector calculation is effected to obtain magnetic instructions, and therefore the method requires provision of a vector's rotational position detecting section, a vector calculating section, and a magnetic flux control section. Accordingly, the method is necessarily intricate, and is not practice in the field of small capacity motors.